1. Field of the Invention
The present invention relates to a developing device for storing therein a developer material composed of toner particles and carrier granules. The device supplies the developer material onto a surface of a photoreceptor in order to visualize an electrostatic latent image formed on the surface of the photoreceptor provided in an electrophotographic printing machine such as a copying machine.
2. Description of the Prior Art
Developer devices for visualizing ( developing ) an electrostatic latent image formed on the surface of a photoreceptor using a developer material composed of carrier granules and toner particles are used, for example, in many dry-type copying machines. In such developing devices, the quantity of the toner particles is reduced while being used in the developing process; whereas, the quantity of carrier granules in the developer material remains the same. Therefore, the quality of the carrier granules being stirred with toner particles in the developer vessel deteriorates because a resin coating layer on the surface thereof is peeled, or toner particles adhere onto the surface thereof. As a result, the charging ability of the developer material gradually deteriorates, thereby presenting the problem that the copied image quality deteriorates.
A device designed for the trickle system which prevents the deterioration of the charging ability by supplying additional carrier granules separately from the refill for the used toner particles is disclosed (see, for example, Japanese Laid-Open Patent Application No. 21591/1990 (Tokukouhei 2-21591)). In such a device, when adding additional carrier granules, excessive developer material in the developer vessel overflows and is discharged through a discharge opening formed on the side face of the developer vessel to be collected in a collecting case. By repeating the above refill and discharge of the developer material, the developer material in the developer vessel whose charging ability has deteriorated can gradually replace. Thus, the required charging ability of the developer material can be maintained, and the copied image quality is prevented from being lowered.
However, in the above developing device, the developer material in the developer vessel overflows and is discharged through the discharge opening provided on the side face of the developer vessel. Thus, depending on the tilt of the developing device, a quantity of the developer material to be discharged through the discharge opening changes. For example, when moving the copying machine, as being tilted, a large quantity of the developer material may be discharged through the discharge opening at one time, or an appropriate quantity of the developer material in the developer vessel may not be discharged. If this occurs, there arises a great difference from appropriate quantity of the developer material in the developer vessel, thereby presenting the problem that the copied image quality is lowered.
More specifically, when moving the copying machine, if the copying machine is tilted in the direction where the discharge opening is placed at lower position than the reference position, a large quantity of the developer material is discharged through the discharge opening, and the quantity of the developer material in the developer vessel becomes much less than the appropriate quantity. The above situation may occur even after the copying machine is moved if the developing device is being used in the above tilted position.
If the above situation occurs, the charging ability of the developer material deteriorates, thereby presenting the problem that the copied image quality is lowered. Moreover, in the case of controlling the ratio of the toner particles to the carrier granules by the output from a permeability sensor, the ratio of the toner particles cannot be detected accurately due to a reduced quantity of carrier granules in contact with the permeability sensor, thereby presenting the problems that the ratio of the toner particle drops and the image density is reduced. Furthermore, if the quantity of the developer material in the developer vessel is greatly reduced, a magnetic brush may not be formed, and therefore the developing process may not be carried out desirably. Moreover, the image may be blurred, or the image may not be developed. Furthermore, even after the tilt of the developing device is set back to the horizontal position, an appropriate quantity of the developer material cannot be achieved immediately, and thus a desirable quality of the copied image cannot be ensured for a while.
On the other hand, if the developing device is being used in the tilted position in the direction where the discharge opening is placed at upper position than the reference position after the copying machine is moved, the developer material is not discharged through the discharge opening, and thus an excessive quantity of the developer material exists in the developer vessel.
If this occurs, the drive torque for driving a developer material supply section provided in the developer vessel increases, and the developing device may not be activated properly, thereby presenting the problem that the developer material may not be supplied onto the photoreceptor surface appropriately. Furthermore, in the case of controlling the ratio of the toner particles to the carrier granules by the output from the permeability sensor, the quantity of the developer material becomes excessive with respect to the appropriate quantity, thereby presenting the problem that the copied image quality is lowered.
Namely, in the arrangement where the developer material overflows and is discharged through the discharge opening, if the developing device is tilted, an appropriate discharge of the developer material through the discharge opening may not be ensured, and thus the developer material may not be supplied onto the photoreceptor surface appropriately, thereby presenting the problem that the copied image quality deteriorates.